A computer-based system is proposed that will use cognitive event-related potentials (ERPs) to assess the drowsy state and to detect sleep onset. It will combine ERPs with computerized polysomnography (PSG) to provide objective measures of state changes for both sleep-laboratory and research applications. Phase I will be used to determine the ERP components that best reflect differences between drowsiness and alertness, and between waking and sleeping in adults with no sleep-related problems. These subjects will be studied both when alert and when sleep deprived. Recordings will also be made from patients with Obstructive Sleep Apnea (OSA), to define the technical problems that might arise in individuals with disordered waking and sleeping patterns. The goal of the project is to produce equipment for: 1) ERP research on sleep; 2) clinical studies in the sleep lab (for the objective assessment of daytime sleepiness and quality of information processing and for the detection of sleep onset); 3) the home (e.g., for follow-up of treatment effects) using a portable version. For these purposes, ERPs have the important advantage that they can index the cognitive state of the brain, even in sleep, without requiring behaviors that would perturb changes in state. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE